This is a very detailed topic and I am on mobile so I am sure I will leave some things out, but I’ll try to sketch a decent picture. The truth, so far as we could possibly identify it a thousand years later, is that neither one of these narratives is true.

In regards to the first, “proto-colonialism,” the reality is that the Crusades were first and foremost a religious pilgrimage. While there were some, especially among the nobility (aka “the barons”) who clearly were seeking personal gain, such as Bohemond of Taranto or Baldwin of Bolougne, a great many participants had no intention of remaining in the Levant upon completion of the crusade. Many simply visited the holy sites and made their way home. Overall, motivations were as individual as each person, but the overall picture is one in which most completed what they believed was their religious duty and, it having been fulfilled, packed up and left. This, of course, left the new crusader states chronically short of manpower. More importantly, it meant that rather than even accidentally becoming a colonial project wherein Francia or Germany was transplanted to Outremer, the native culture absorbed the newcomers and a sort of ‘Franco-Syrian’ identify was slowly established over the next century. Further information on all of the above can be found in Zoe Oldenburg’s The Crusades

Additionally, the Crusades at first merited nothing more than a local response. The leaders of the cities which were targeted of course were alarmed and then were dispossessed or killed, but the first crusade failed to generate any sizable moral or political response in neighboring regions. The response in Mosul was muted, and it was barely noteworthy in Baghdad. The Seljuqs of course fought because it was their land and armies being attacked, but even they were fractured politically and were fighting each other even as the crusaders arrived. The seizure of Jerusalem generated a reaction from Cairo only because the Fatimids had controlled the territory directly, following a lengthy war with the Seljuqs to keep it. After the crusader victory at Ascalon however, they could not even seize the city itself and Fatimids were content to hold on to it for another 50 years. Even Damascus was content to make accommodations with the new arrivals, becoming semi-allied with Jerusalem until the immensely ill-advised decision during the Second Crusade to attack Damascus rather than Edessa as planned. Ultimately it was not until almost a half century after the first crusade that Muslims in Syria and Iraq became galvanized in a significant way toward fighting off the crusader, and a lot of that was due to the personal dynamism of Imad and Nur ad-Din Zengi and contemporary preachers who shamed the people of Mosul and Baghdad into doing something.

In regards to the second, that the crusade was a response to Islamic aggression, this is to be frank an even poorer and more insidious narrative. There was no militarism, aggression, or threat from any Muslims in the area which was conquered by the crusaders, except aggression between competing Islamic polities. This is a fairly straightforward historical truth that was ignored by contemporaries and has become controversial in modern times because of unrelated political and social developments. The origin of the Crusades as an idea developed from military campaigns in Iberia and southern Italy, in which the Papacy officially sanctioned action against Muslim states. It was an established, if nebulous, concept for a couple decades before Alexios Komnenos wrote to Rome asking for military assistance against the Seljuq Turks.

A couple things to make note of in regards to the situation in the Byzantine Empire by the mid 1090s. First, over 20 years had passed since the Battle of Manzikert. Although this is held up as a disastrous moment for the Empire, and indeed was looked upon that way in hindsight by people such as Anna Komnena, the battle itself was less destructive than its aftermath. In fact, it was the political upheaval and internal machinations of the Byzantine elite that led to the collapse of imperial control of Asia Minor. Romanos and the vast majority of his army eventually left the battlefield intact, but civil strife following his usurpation gave the Seljuq’s the opportunity to move into Asia Minor en masse.

By the time of Alexios’s letter, the worst had passed and the situation had been somewhat stabilized. At the very least, it was extremely unlikely that Constantinople would be under direct threat. Furthermore, some of the most desperate fighting in the intervening years had not been against the Seljuqs but instead against invading Normans led by the Guiscard family, which had successful conquered Arab, Lombard, and Greek statelets in Italy. Alexios had fought a fierce war with the Normans throughout the Balkans in order to maintain his European possessions, even as Seljuqs settled comfortably into Anatolia. One of the leaders of the Norman expedition? Bohemond of Taranto.

Second, what Alexios was asking for was not what actually occurred, and the result was certainly not remotely related to Byzantine needs and strategic goals. What Alexios needed and wanted were mercenaries that he could use to begin taking back territory in Asia Minor that had been lost to the Turks. What he emphatically didn’t want or need was the mass of largely unarmed, untrained people who arrived in Constantinople, nor the egos and rivalries of the barons who showed up ostensibly to assist, but with their own agendas both righteous and selfish. There was very little coordination between the crusader armies and the Byzantine army led by Tactikios. Furthermore, as early as the aftermath of the Battle of Doryleum but especially by the time of the Siege of Antioch, it was clear that crusader aims did not align at all with Byzantine. What needed to happen for the security of the Empire to be guaranteed was the seizure and especially the holding of the Anatolian interior so that they could be stabilized and reorganized under imperial rule. However, this was unacceptable to the crusaders for various reasons. The Byzantines did not allow them to plunder the towns they took in Asia Minor, and the Seljuqs did their best to remove and destroy anything of value as they retreated, especially water sources. Most importantly however the crusaders saw their goal as fulfilling a pilgrimage to Jerusalem and so had little interest in staying in what was becoming poor, depopulated land. The severing of Byzantine and crusader goals was completed at Antioch, where both sides became convinced the other was betraying them. In time some crusader states, but especially Antioch, would become an enemy to the empire rather than an ally and asset. In sum, it simply cannot be said that the crusade was a specific, targeted, and effectual response to any Muslim aggression either in intent or in outcome.

Sources for the above include The Alexiad by Anna Komnena, Warren Treadgold’s A History of the Byzantine State and Society, Steven Runciman’s The First Crusade, and Carole Hillenbrand’s The Crusades: Islamic Perspectives

To be honest, neither of them are very appropriate because they completely neglect the complicated context and manifold traditions that the crusading ideology arose from, not least the intense religiosity of the period.

I'm going to do an analysis of the origins of the Crusading ideology - where it came from, how it was expressed etc. I'm going to do this because of how important and varied the context is, which has to be covered before I answer the question. I might come back later and do more, but it's 1am as I start to write this, and I have to drive my a friend to his gig in the morning.

Note: When I say Christian, I will be referring to that of Catholic Europe, any references to Orthodox Christianity and the Byzantine Empire that it primarily existed under will be explicitly labeled.

The Birth of Crusading Tradition

The First Crusade can can be described in various ways – a quest for spiritual redemption, a sanctified outlet for the endemic violence of the European martial classes, and an unprecedented outbreak of religious intensity; what all of these elements have in common is that they exist within the ideological realm. Those who participated in the Crusade were motivated to travel thousands of miles to fulfil the vow that they took voluntarily and as such its hard to overstate the significant of mindset and outlook of the participants - the ideological realm plays a huge part in this.

Christendom on the eve of the Crusades

Evidence for how Muslims were perceived:

Conception of Muslims in literature

Main Sources: Concerning Heresy by John of Damascus and The Apocalypse of Pseudo-Methodius

Muslims were not framed in a complementary manner within the Christian worldview. There were pre-existing religious texts that tackled the issue of apparent Muslim success at Christianity's expense.

• Whilst the Church continued to produce rhetorical weapons against Islam (e.g. the translation of the Koran into latin in 1143 - they title it 'The word of the false prophet Muhammed'), there were some texts that were enduringly popular for several centuries before the First Crusade.
• Concerning Heresy by John of Damascus and The Apocalypse of Pseudo-Methodius had been translated into several vernacular languages (something that took time, effort and interest) and remained enduringly popular throughout this period; so their arguments struck a chord with their readers. It should be noted that the readers were the small proportion of the population who were literate.
• Pseudo-Methodius framed the Muslims within God’s divine plan – they are being used to punish Christian sinners rather than being favoured. A doctrinal approach.
• John of Damascus’ polemic gives the impression that it engages with the actual text of the Qur’an. A direct refutation. It also tries to depict the followers of Islam as heretics and pagans for rhetorical effect.
• Needless to say both these texts discuss the primacy of Christianity and the wicked nature of Muslims.

Conception of Muslims in vernacular oral poetry

Main Sources: The 'Chanson de Roland'; the ‘Poema de Mio Cid’.

Muslims were already stylised in popular literature as a grand archetypal villain.

• The ‘Chanson de Roland’ is particularly notable for this – despite the historical fact that Charlemagne’s rearguard was annihilated by Basques (the historical inspiration for the poem) an epic poem needs an exotic and epic foe.
  • This is both representative of and a stimulus for the race hatred; representative in the fact that the poem was composed several centuries after the events which it describes and whilst it vilifies Muslims the contemporary sources of Roland’s death are far more prosaic in their description of Islamic culture. A stimulus for the hostility as it stereotypes Muslims as evil and the vast majority of the populace would never meet a Muslim in a situation that would contradict this. It was translated into several vernacular languages, showing how it was influential, and in the form of traditional oral poetry this work was easily accessible for the masses in an age of mass illiteracy.
• Also notable is the ‘Poema de Mio Cid’ – another of the great chanson de geste.
  • Here, Moorish society is portrayed as extremely wealthy (i.e. avaricious and morally corrupt) and ‘ganancias’ or booty is a prominent theme throughout the poem and a significant motive for its titular character.
  • The Muslims are portrayed as extremely greedy, which results in them repeatedly falling for El Cid’s tricks. E.g. they are tricked into rushing out of their stronghold to take El Cid's camp as they want booty and fear that other Muslims will take it first.
  • Here, I would argue that a lust for loot might have had primacy in the populace’s mind whenever they considered fighting the Muslims; but that it was their very nature as enemies of the faith that made them perfectly acceptable targets in the first place.
• We don't know for sure when these epic were composed, ‘Chanson de Roland’ could have been created before the First Crusade but ‘Poema de Mio Cid’ likely wasn't. However, both of these works are evidential of pre-existing stereotypes, otherwise they would not be used so boldly in the text without a single hint of characterisation. The poems were enduringly popular among audiences after all.

The Inception of the Crusade

Main Sources: Western Society and the Church in the Middle Ages by R. W. Southern; The First Crusade: The Call from the East by Peter Frankopan; God's War: A New History of the Crusades by Christopher Tyreman; The Two Cities: Medieval Europe 1050-1320, 2nd Edition; How to Plan a Crusade by Christopher Tyreman; The Crusades: 1095-1198 by Johnathan Riley-Smith in The New Cambridge Medieval History Volume 4 Part 1; The First Crusade and the Idea of Crusading by Johnathan Riley-Smith.

Church Context and Motivation for the Crusading Ideology

• The casus belli was the invasion and occupation of most of Asia Minor by the Turks. The threat posed led the Byzantine Emperors in Constantinople to appeal for aid from popes and important laymen in the west.
  • The First Crusade was called for in November 1095, but as far back as 1074 Pope Gregory VII proposed to lead an army of 50,000 men east. In 1089/1091 it's possible Pope Urban was considering calling for French and other volunteers to help the Greeks; and in 1090 the Count of Flanders entered into an agreement to serve the Byzantines with 500 knights for pay.
  • This means that there were pre-existing initiatives underway to help Orthodox Christians in the east, so there was already some semblance of tradition. In the same way this can be viewed as a continuation of the Byzantine tradition of using foreign forces adeptly with their tremendous wealth (but more on that later).
• When Pope Urban II called for the First Crusade in response to a Byzantine plea, he proposed a much more ambitious strategy - the recapture of Jerusalem. This wasn't new either.
  • This had been already been discussed in papal circles for some time: in 1074 Pope Gregory VII suggested that the same expedition could liberate Jerusalem; Alexios I (the current Byzantine Emperor) suggested aid to Jerusalem in his letters to French nobles and ther is some evidence that Peter the Hermit had begun to summon the French for this same aim before the First Crusade was even called for.
• The Church was already supporting a was against the Muslims in Sicily and Spain and had been using the term 'liberation' for it.
  • From the beginning of his time as Pope, Urban II had been backing a drive to occupy Tarragona (a city 50 miles south of Barcelona).
  • He had already suggested that those planning a pilgrimage to Jerusalem should instead try and restore Tarragona where they could get the same spritual benefits.
• At Clermont, where the Crusade was first preached, Urban proposed two war aims: the salvation of the eastern christians (people) and the salvation of Jerusalem (a place). This has to be viewed in the context of the eleventh century reformation that was happening in the west.
  • The Papacy had split with the Holy Roman Empire, and with Imperialists occupying Rome and the Pope residing in exile, the reformers in control of the Papacy had turned to sympathetic nobles for military support. This was building on the idea of milites sancti Petri that Pope Gregory VII had espoused, wherein he imitiated the standard fealty between a bishop and his vassals by putting forward the idea of a body of knights, scattered throughout Christendom, who were bound by duty to the Churhc and the Pope as its head.
  • This in turn led to a need for the Church having a spiritual basis by which to sanctify the use of violence, a number of scholars had been doing research into this and the most eminent among them was Anselm of Lucca.
• All these things build into the fact that the Papacy was just exiting a period of being weak(er) that it had been historically.
  • The issues with the Holy Roman Empire notwithstanding, there was also monastic reform, new heretical movements, new applications of logic to theology and endemic warfare between Christian nobles/rulers.
  • The Church had many threats within, as well as without and a Crusade was an outlet that solved many of these issues in one fell swoop by granting the Papacy a significant method of projecting power.
• The goal of Jerusalem synthesised the traditions of warfare and pilgrimage and formalised the concept of penitiential warfare.
  • This strengthened to the appeal significantly, as pilgrimages had become increasingly popular over the previous century. It had done so even in the face of disapproval from some quarters of the Church - which should give you an idea of how strong a grip it held on the minds of the general populace, as many, many, other trends did not survive the Church's disapproval.

Urban II's Specific Theology of War for the First Crusade

Main sources: War, peace and Christian order by Ernst-Dieter Hehl in The New Cambridge Medieval History Volume 4 Part 1; The First Crusade and the Idea of Crusading by Johnathan Riley-Smith;* Western Society and the Church in the Middle Ages by R. W. Southern; God's War: A New History of the Crusad*es by Christopher Tyreman.

• The call for the First Crusade was based on the presupposition that under specific circumstances, participation in a military campaign was not a sin.
  • We can see this as he offers spiritual rewards for the endeavour.
• In this war, the crusaders were directly obeying the will of God.
  • Guibert of Nogent names his chronicle, 'The Deeds of God through the Franks' (Gesta Dei per Francos).
  • The crusaders often described themselves as 'the army of God' (exercitus Dei).
  • The fact that the expedition encoutered great difficulties only served to make the victory seem miraculous and strengthen the belief.
• As I mentioned earlier, Urban II had already framed previous territorial acquisitions from the Muslims as the will of God.
  • He describes the Norman Conquest of Sicily and the Reconquista in this way.
  • In 1091 he quoted Daniel (2:21): 'he changeth the times and the seasons; he removeth the kings, and setteth up kings' to describe how God was turning His face back Christians as they regained his favour.
• Urban's ideas cast the past in a negative light, all of Christendom's losses to Muslims were a result of the sins of Christians, so an effort to retake said lands must involve penance. Thus, he promised the crusading indulgence and created the crusading vow.
  • The precise conditions for the vow were not granted for the warlike deeds themselves but for personal attitude.
  • Only those who went to Jerusalem 'solely from the devotion of God' to liberate the church would receive it.
  • This was the only way the war could be both just and holy in the eyes of God.
  • This would have driven home to anyone who considered signing up for greed, that he would be going against the will of Christ's representative on earth if he did so.
• It's also important to recognise how Urban was redefining penance.
  • Beforehand, you went to confession, reconciled with the Church and then went and did your penance. The spiritual rewards came from the self-punishment.
  • Now, the reward came from offereing one's life for a cause pleasing to God. This meant that not only did the penace of a crusade purify you in the eyes of the Church, it did so directly in the eyes of God as you did his will.

The Response

Main Sources: Western Society and the Church in the Middle Ages by R. W. Southern; The First Crusade: The Call from the East by Peter Frankopan; God's War: A New History of the Crusades by Christopher Tyreman; How to Plan a Crusade by Christopher Tyreman; The Crusades: 1095-1198 by Johnathan Riley-Smith in The New Cambridge Medieval History Volume 4 Part 1; The First Crusade and the Idea of Crusading by Johnathan Riley-Smith;* The Social Structure of the First Crusade by Conor Kostick, Holy Warriors: A Modern History of the Crusades by Johnathan Phillips; The First Crusa*de by Thomas Asbridge.

• Before going in depth to this, there's a historiographical theory known as the Second Son theory that I want to deal with. Basically, it says that a whole load of the crusaders went primarily because of the promise for material wealth. It's been thoroughly debunked by historians but I feel I should tackle it because I see it crop up now and again. In short:
  • Too few of the crusaders were important enough in society to expect to gain anything meaninful in the way of spoils.
  • Nowhere near enough of the Crusaders actually stayed in the Holy Land afterwards. They went home because they had fulfilled there oath so they were done. You see evidence of this later, when the Papacy issues a bull calling for more settlers to go to the Crusader Kingdoms in the Holy Land because their population is too low.
  • When they came back, most crusaders had gained nothing tangible from their endeavours apart from the relics that appeared in churches all across western europe.
• When the First Crusade was called at Clermont, the association of war and pilgrimage meant that any control the Papal actors had over who would go on crusade was lost. It is here where we can gather evidence for the motivations of the crusaders.
  • Urban had taken steps to ensure that only nobles and knights were recruited, so obviously what he intended was an elite core of western european warriors as the crusade.
  • However, pilgrimage had always been open to everyone as a penance. The Pope simply could not refuse any layman or woman who wanted to take the cross.
  • Added into this mix, was the fact that Jerusalem itself was the goal. Jerusalem was, quite simply, the most charismatic penance then known.
• The response itself was gigantic.
  • An estimate for the number of individuals who took the cross for the three waves of the First Crusade between 1096 and 1101 is about 136,00, of which fewer than 10% of these would have been nobles.
  • In addition to this, the journey and the following campaign, along with the danger and general unpleasantness, were incredibly expensive. A French Knight might well have had to think of spending four to five times his annual income.
• This brings the question of motivation up. Why did they go? The answer primarily lies in the spiritual rewards on offer.
  • I reiterate that it's difficult to underestimate the intensity of religious feeling of the period. Men and women laboured under a terrible burden of guilt, constantly reminded by clergy that they were locked in a sinful world and their only hope for their soul was through salvation via Christ.
  • This, having had years and years to entrench into cultural attitudes and religious relations meant that the appeal was incredibly potent. Not only could one strike a blow for one's Christian cousins, groaning under the burden of Muslim rule in the east, or for Christ himself, who's patrimony had been stolen in the 'occupied' Holy Land; but one could also purify the souls of their dead relatives in addition to that of one's own.
  • This had consequences lasting into the next life for a crusader and their loved ones, as well as supporting their religion as a whole.

Conclusion

In short, you can see how, in the end, absolutely everything is couched within the religious framework of the day once you dig deep enough. The literature's objection to Muslims was that either that they weren't Christian, or that they were immoral - which was judged by the standards of the Bible; the Crusading ideology itself was born out of movements within the Catholic Church and crystallised by Urban II; and the response was for primarily spiritual reasons.

Proto-colonialist Christendom just doesn't work in this spiritual context. Defensive campaigns against Islam are more tricky, but it doesn't really apply either as:

1. Jerusalem had been in Muslim hands for hundreds of years already (since 638) and that was undboutedly the main objective.
2. The wider trends that helped give birth to the crusading movement had slowly developed over decades, and were not a response to any specific event.
3. When you combine Urban II's theology for the war with the fact that most Crusaders went for spiritual purification, then you have to view it as less of a defensive war against Islam, but more of a war to save Christianity. It was their own sin, their own lack of favour from God that was the issue. The success/threat of Islam was, to them, merely symptomatic of this underlying cause.

Anyway, I'm off to bed. I probably won't be able to check this for about half a day, but please to tell me if you find a mistake.

I hope this answer is useful.

Hey! Unfortunately I'm out on the river for the weekend and can't write up a longer response, but you may be interested in the FAQ, in particular this answer I wrote on whether or not the First Crusade was understood as a defensive war.